Water separators for separating product water from a fuel cell, fuel cells including a water separator and motor vehicles including fuel cells are known in general. For example, one such water separator is described in DE 10 201 2 020 280 A1.
Fuel cells make use of the chemical reaction of a fuel cell with oxygen to generate electricity. For this purpose, fuel cells include as the core component the so-called membrane electrode assembly or unit (MEA), which may be designed as an assemblage of the membrane, which conducts ions, in particular protons, and an electrode (anode and cathode) situated on each side of the membrane. The active material may contain a catalyst or comprise a catalyst which facilitates the chemical reaction. Furthermore, gas diffusion layers may be situated on the sides of the electrodes facing away from the membrane on both sides of the membrane electrode assembly. The fuel cell has at least one membrane electrode assembly or a plurality of membrane electrode assemblies, which may be situated in a fuel cell stack, the powers of a plurality of membrane electrode assemblies being additive. During operation of the fuel cell, an operating medium, for example, the fuel, in particular hydrogen (H2) or a gas mixture containing hydrogen, is supplied to the anode, where H2 is oxidized electrochemically to H+ and releases electrons. Water-bound or waterless transport of the protons H+ out of the anode space into the cathode space takes place across the membrane, which separates reaction spaces of the fuel cell from one another in airtight, gas-tight manner. The electrons made available at the anode are supplied to the cathode via an electrical line. The cathode receives another operating medium, for example, oxygen (O2) or a gas mixture containing oxygen, so that O2 is reduced to O2− with an uptake of the electrons. At the same time, these oxygen anions in the cathode space react with protons transported across the membrane to form water. Due to the direct conversion of chemical energy into electricity, fuel cells achieve an improved efficiency in comparison with other electricity generators because they bypass the Carnot factor.
When operation of the fuel cell is stopped and the motor vehicle including the fuel cell is parked, for example, product water present in the separator tank is preferably drained out. This prevents the product water from freezing in the water separator at low temperatures below the freezing point of water and thereby clogging the outlets. In other words, if the outlets are closed, then any new product water generated when operation of the fuel cell is resumed cannot flow out of the separator tank, so the tank may overflow. In particular the primary outlet may clog due to freezing product water. If, after stopping operation of the fuel cell, there is no product water, at least inside the riser pipe, then, beyond a predetermined fill level of the separator tank, product water newly directed into the separator tank may pass through the riser pipe to the secondary outlet.
Even if the separator tank is emptied during or after stopping operation of the water separator, condensate may form during cooling of the water separator or other parts of the fuel cell, which may flow into the separator tank and possibly freeze there. To prevent freezing of the condensate in the primary outlet, thereby clogging it, the sealing element may close the primary outlet and thus prevent freezing condensate, which might be formed later, from penetrating into the primary outlet.
However, the uptake capacity for product water of a known water separator is limited by the sealing element and the riser pipe, so that separator tanks of known water separators must have larger dimensions in order to be able to hold the same amount of product water as water separators in which neither the riser pipe nor the sealing element is situated in the separator tank. In particular, when the fuel cell is to be used in a motor vehicle, the installation space available for the fuel cell is limited, so that the collecting tank cannot readily be enlarged.